1. Field of the Invention
The present invention relates to an image processor which receives color image data and converts them to image data used for image forming.
2. Description of Prior Art
Color image data of red, green and blue are converted to image data of cyan, magenta, yellow and black for image forming. It is known to discriminate black character areas in the input color image data and to the black component is subjected to edge emphasis and the cyan, magenta and yellow components are subjected to erase edges.
In order to improve reproducibility of edges of black characters in a color image, it is proposed to eliminate cyan, magenta and yellow components at the character edges. That is, a minimum of the three components is substituted to prevent partial whitening around the black characters. An amount of edge correction on edge emphasis of black component is obtained by a spacial filter of lightness data for expanding the characters in order to improve reproducibility of black characters. On the other hand, in areas discriminated as black characters, the amount of black paint for the black component is set to 100% to increase the density of black characters.
However, even in the proposed processing, the density of black characters is insufficient, and the characters are reproduced with densities smaller a little than the original document. If the amount of edge emphasis is increased further, a sufficient effect is observed though the contrast at the edges of the black characters is enhanced.